This invention relates to a catalytic technique for upgrading olefin streams rich in dienes to heavier hydrocarbons rich in aliphatics and aromatics. In particular, it provides a continuous process for oligomerizing a feedstock containing monoalkenes and dienes to produce C.sub.5.sup.+ hydrocarbons, such as liquid fuels, isobutane, aromatics and other useful products. Diene-containing liquids, such as thermal cracking liquids, are useful feedstock herein.
Developments in zeolite catalysis and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks for producing C.sub.5.sup.+ gasoline, diesel fuel, etc. In addition to basic chemical reactions promoted by ZSM-5 type zeolite catalysts, a number of discoveries have contributed to the development of new industrial process. These are safe, enironmentally acceptable processes for utilizing feedstocks that contain olefins. Conversion of C.sub.2 -C.sub.4 alkenes and alkanes to produce aromatics-rich liquid hydrocarbon products were found by Cattanach (U.S. Pat. No. 3,760,024) and Yan et al (U.S. Pat. No. 3,845,150) to be effective processes using the ZSM-5 type zeolite catalysts. In U.S. Pat. Nos. 3,960,978 and 4,021,502, Plank, Rosinski and Givens disclose conversion of C.sub.2 -C.sub.5 olefins, alone or in admixture with paraffinic components, into higher hydrocarbons over crystalline zoelites having controlled acidity. Garwood et al. have also contributed to the understanding of catalytic olefin uprgrading techniques and improved processes as in U.S. Pat. Nos. 4,150,062, 4,211,640 and 4,227,992. The above-identified disclosures are incorporated herein by reference.
Conversion of olefins, especially propene and butenes, over HZSM-5 is effective at moderately elevated temperatures and pressures. The conversion products are sought as liquid fuels, especially the C.sub.5.sup.+ aliphatic and aromatic hydrocarbons and C.sub.4 hydrocarbons, in particular iso-butane. Product distribution for liquid hydrocarbons can be varied by controlling process conditions, such as temperature, pressure and space velocity. Gasoline (C.sub.5 -C.sub.10) is readily formed at elevated temperature [(e.g., up to about 700.degree. C.)] and moderate pressure from ambient to about 5500 kPa, preferably about 200 to 2900 kPa. Olefinic gasoline can be produced in good yield and may be recovered as a product or fed to a low severity, high pressure reactor system for further conversion to heavier distillate-range products. Distillate mode operation can be employed to maximize production of C.sub.10.sup.+ aliphatics by reacting the lower and intermediate olefins at high pressure and moderate temperature. Operating details for typical "MOGD" oligomerization units are dislcosed in U.S. Pat. Nos. 4,456,779; 4,497,968 (Owen et al.) and 4,433,185 (Tabak), incorporated herein by reference. At moderate temperature and relatively high pressure, the conversion conditions favor distillate-range product having a normal boiling point of at least 165.degree. C. (330.degree. F.).
Many feedstocks of commercial interest, such as thermal cracking byproduct, etc., contain both mono-olefins and diolefins (e.g. C.sub.2 -C.sub.6 mono-alkenes and C.sub.4.sup.+ dienes) along with C.sub.1 -C.sub.10 light aliphatics, and a minor amount of aromatics. Gaseous and liquid streams containing dienes are typically produced in thermal cracking operations. One common example is pyrolysis gasoline, which is produced as ethene (ethylene) byproduct. Such diene-containing streams are often difficult to process due to poor thermal stability and the tendency of dienes to form coke and gum deposits. This complicates preheating of such streams into the high temperatures required of most catalytic upgrading processes. Prior attempts to upgrade such materials have pretreated the feedstock to hydrogenate the diolefin selectively, as in U.S. Pat. No. 4,052,477 (Ireland et al). The present invention is concerned with providing a safe and low cost technique for catalytically converting diene-rich streams to high value C.sub.4.sup.+ products rich in aromatics.
It has been found that diene-containing olefinic light hydrocarbons can be uprgraded directly to liquid hydrocarbons rich in C.sub.5.sup.+ aliphatics and aromatics by catalytic conversion in a turbulent fluidized bed of solid acid zeolite catalyst under high severity reaction conditions without deleterious effects from the diolefin components. This technique is particularly useful for upgrading C.sub.4.sup.+ liquid pyrolysis products, which may contain minor amounts ethene, propene, C.sub.2 -C.sub.4 paraffins and hydrogen produced in cracking petroleum fractions, such as naphtha, ethane or the like. By upgrading the complex olefinic by-product, gasoline yield of cracking units can be significantly increased. Accordingly, it is a primary object of the present invention to provide a novel technique for upgrading diene-rich hydrocarbon steams.